A sample measurement device is a device that individually measures a plurality of samples. Representative sample measurement devices include a liquid scintillation counter. The liquid scintillation counter has a rack-transporting mechanism which transports a rack holding a plurality of sample containers, a measurement unit which measures light caused by a radioactive substance contained in each sample container, a container transporting mechanism which transports the sample container between the rack and a measurement chamber unit, or the like. In the sample container, in addition to liquid sample, liquid scintillator is included. When a radiation (for example, a β ray) is emitted from the radioactive substance in the sample, light emission in the liquid scintillator is caused by the radiation. The light is detected by a pair of photomultiplier tubes forming the measurement unit.
In general, a shielding structure must be provided in order to block an extrinsic radiation at a periphery of a measurement chamber which stores the sample container to be measured. Such a shielding structure is formed from a metal which is very heavy. Therefore, it is more preferable that the shielding structure be placed below a rack placement surface rather than being placed above the rack placement surface. In addition, when a system is employed in which the sample container is transported upward from the rack, because a shaft which supports the sample container would exist within a lifting/lowering path during the measurement, there is a problem in that light shielding in the lifting/lowing path is difficult. Therefore, it is desired that the measurement chamber be provided below the rack placement surface, and also to withdraw the sample container downward from the rack.
Patent Document 1 discloses a liquid scintillation counter of the related art. In the liquid scintillation counter described therein, the measurement chamber is provided above a transport table for transporting the rack. Patent Document 2 discloses a rack transporting device which can be used for the liquid scintillation counter or the like.